1. Field of the Invention
The present invention relates to a photosensitizer in which a dipyrromethene boron complex compound having a specific structure is used, and a visible light curable resin composition which contains the above-mentioned photosensitizer and hence shows a high sensitivity to a light in a visible light range.
Furthermore, the present invention relates to a visible light curable resin composition in which the prevention effect of curing by oxygen is improved and which can exhibit a high sensitivity to a light in a visible light range and is excellent in curing properties.
In addition, the present invention relates to a visible light curable resin composition which can be used under the irradiation environment of a specific safelight.
2. Description of the Related Art
In recent years, in the field of information or image recording which utilizes a photopolymerization reaction, there has been investigated a technique where a manuscript electronically edited by a computer can be directly output and recorded by the use of a high power laser, in place of the conventional recording technique of a film manuscript or the like by an ultraviolet light. The above-mentioned recent technique has an advantage that direct writing is done by the laser, so that recording and image-formation steps can be remarkably simplified.
Nowadays, much of high-power and stable laser light sources which have usually been used possess output wavelengths in a visible light range. Concretely, an argon laser having stable oscillation lines at wavelengths of 488 nm and 514.5 nm and a YAG laser having a bright line at 532 nm as a second harmonic are often used. Therefore, a compound having a high sensitivity to these wavelengths has been desired, but a conventional photosensitizer for the ultraviolet light cannot be used because of a low sensitivity in the visible light range. Moreover, by the addition of a pyrylium salt or a thiopyrylium salt, the sensitivity in the visible light range can be improved, but a photosensitive layer containing such a compound is poor in storage stability, which makes its use difficult.
As compounds having photosensitivity in the visible light range, there are known, for example, 7-diethylamino-3-benzothiazoylcoumarin (trivial name: coumarin-6) and bis[3-(7-diethylaminocoumaryl)] ketone (trivial name: ketocoumarin), but these compounds have maximum absorption wavelengths in the vicinity of 450 nm, which is shorter than 488 nm of the argon laser, and hence the photosensitivity is insufficient. In addition, a 4-substituted-3-benzothiazoylcoumarin compound described in Japanese Patent Application Laid-Open No. 18088/1992 has the high photosensitivity at 488 nm of the argon laser, but it scarcely has absorptions at 514.5 nm and 532 nm that is the second harmonic of the YAG laser. Thus, this kind of compound is poor to sufficiently improve the photosensitivity.
European Patent No. 0619520, U.S. Pat. No. 5,498,641, Japanese Patent Application Laid-Open Nos. 258444/1997, 179504/1996, 95244/1996, 76377/1996, 6245/1996, 225474/1995, 219223/1995, 5685/1995 and 241338/1993 disclose bispyrromethene boron compounds, but these compounds are poor to sufficiently improve the sensitivity to the above-mentioned laser light and the storage stability of the photosensitive layer.
On the other hand, a conductor circuit such as a printed-wiring board has been heretofore formed by exposing and developing the board coated with a photosensitive resist to prepare a resist pattern, and then removing unnecessary portions therefrom by etching.
With regard to an exposure technique, there are a method of exposing the board through a photo mask, and another method of directly drawing a resist by a laser. In the method of exposing the board through the photo mask, there are a problem that extensive time is taken for the positioning of the photo mask, and another problem that when the surface of the resist is tacky, the positioning of the photo mask is more difficult.
In the method of directly drawing the resist by the laser, this resist is required to be highly sensitive, because an exposure time is very short. Accordingly, it has usually been conducted to cover a resist surface with an oxygen-blocking layer such as a cover coat or a cover film so that active radicals generated by the irradiation of the laser may not be deactivated by oxygen in air, whereby oxygen can be blocked and hence the high sensitivity can be maintained. However, this operation is inconveniently troublesome.
Moreover, in the case that the above-mentioned visible light curable resin composition which can be cured by the visible light is handled, an electric lamp such as a fluorescent lamp colored by coating an outer tube of the lamp with a dark red colorant or by winding a dark red film around the outer tube is used as a safelight (a working lamp). Under the environment of such a dark red safelight, however, some problems are present. For example, it is difficult to inspect the state of a coated film after the coating, and it is not easy to inspect a coating device, an irradiation device, a conveying device and the like. In consequence, safe working properties, working efficiency, the quality stability of products and the like are poor. In addition, in the case that an uncolored fluorescent lamp is used as the safelight, the working environment is lightened and there are not the above-mentioned problems any more, but even portions where the exposure is not required might be exposed inconveniently, depending on the kind of photosensitive resin.